## January 2007

# James Clerk Maxwell

James Clerk Maxwell (1831 - 1879) was a 19th century Scottish physicist who demonstrated that electric and magnetic forces are two aspects of electromagnetism. He further showed that electric and magnetic fields traveled through space, in the form of waves, at a speed of 3.0E5 k/s. He thus argued that light was a form of electromagnetic radiation.

Maxwell codified earlier work on electricity and magnetism by Michael Faraday, Andre Marie Ampere, and others into a linked set of twenty differential equations in quaternions, the same mathematical system used later by Einstein for the relativity theory. Both theories have many similarities and we can say that Maxwell's theory of electromagnetism was a precursor of the relativity. Heaviside simplified the theory down to four differential equations, known collectively as Maxwell's Laws or Maxwell's equations. Maxwell's Laws describe the nature of static and moving electric and magnetic charges, and the relationship between the two, namely electromagnetic induction. The equations allow for the existence of a self-propagating electromagnetic wave which has the same velocity as that of light, suggesting that light is in fact that electromagnetic wave. The validity of that suggestion was later demonstrated in experiments by Heinrich Rudolf Hertz, and was fundamental to the invention of radio, usually attributed to Guglielmo Marconi.

Maxwell also did basic work on Thermodynamics which led him to the well known thought experiment, Maxwell's demon.

The Special Theory of Relativity owes its origins to Maxwell's equations of the electromagnetic field -- Albert Einstein. There is a mountain range on Venus, Maxwell Montes, named after James Clerk Maxwell.

Upon arriving at Cambridge University, he was told there would be a compulsory 6am church service (now discontinued, fortunately!) He stroked his beard thoughtfully, and slowly pronounced, in a thick Scots Brogue, "Aye, I suppose I could stay up that late"

Posted by Jay Roberts at 07:09 PM | Permalink

**Hans Christian Orsted **

Hans Christian Ørsted (1777-1851) was a physicist and chemist of Denmark, influenced by the thinking of Kant. In 1820 he discovered the relationship between electricity and magnetism in a very simple experiment. He demonstrated that a wire carrying a current was able to deflect a magnetized compass needle. Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework.

In 1825 he made a significant contribution to chemistry by producing aluminum for the first time.

Posted by Jay Roberts at 06:52 PM | Permalink

**William Gilbert**

Published the celebrated treatise entitled De Magnete(On the magnet) in 1600. This was the first comprehensive study of magnetism and took 17 years to complete. Gilbert dedicated it to those who look for knowledge "not only in books but in things themselves." The growing interest in compass navigation may have influenced Gilbert somewhat because he wrote De Magnete at the time the English were preparing to meet the Spanish Armada. Gilbert lived from 1544 to 1603, roughly the same period as Johannes Kepler. In 1600, when De Magnete was published, Giordano Bruno was burned at the stake in Rome because he believed in the Copernican theory. It was also the year in which Johannes Kepler set out to join Tycho Brahe in Prague.

Gilbert, a student of medicine, received his M.D. at Cambridge University in 1569, and by themid-1570s was a prominent physician in London. In 1600 he became president of the Royal College of Physicians and was appointed as personal physician to Queen Elizabeth I. When she died in 1603, her only personal legacy was a grant to Gilbert to pursue his hobby, physics, but he had little time to enjoy it because he was a victim of the plague a few months later.

For his work on magnets, Gilbert became known as the "Father of Magnetism." He discovered various methods for producing and strengthening magnets. For example, he found that when a steel rod was stroked by a natural magnet the rod itself became a magnet, and that an ion bar aligned in the magnetic field of the earth for along period of time gradually developed magnetic properties of its own. In addition, he observed that the magnetism of a piece of material was destroyed when the material was sufficiently heated.

One of Gilbert's major discoveries (he credited himself with 21) was that the earth is a huge magnet, a connection that Peregrinus failed to make. He proved that a compass needle swings north because of the magnetism of the earth itself and not - as some believed - because of a star in the Big Dipper or a mysterious range of iron-capped mountains in the North. Using a spherical magnet and magnetic needle that was free to rotate in a vertical plane that included the magnetic poles of the sphere, he found that the needle dipped below the horizontal (the tangent plane to the sphere) at different angles, depending on its position on the sphere. Gilbert realized that lines joining points of constant magnetic declination (the angle between the magnetic needle and the horizontal) were also lines of constant latitude on a sphere. Impressed with his discovery, he suggested an application to navigation. Although navigators used compasses at sea, they knew that variations in the earth's magnetism often caused a compass to be unreliable. Gilbert thought circles indicating constant magnetic dip on the earth might be more reliable. However, navigators soon found that the dip along latitude lines varied considerably, and so the idea was abandoned.

Although he is chiefly noted for his work in magnetism, Gilbert made many important contributions to the science of electricity, ranging from the invention of the electroscope to the study of conductors and insulators. To him we owe the term "electricity." He also left a large manuscript devoted to speculative work in general science, which was published posthumously in 1651.

Galileo said De Magnete made Gilbert "great to a degree that is enviable." The inscription on Gilbert's tomb is more modest. It reads: "He composed a book, concerning the magnet, celebrated among foreigners and among those engaged in nautical affairs."

William Gilbert set out to debunk magical notions of magnetism, yet in building an intellectual bridge between natural philosophy and emerging sciences, he did not completely abandon reference to the occult. For example, he believed that an invisible "orb of virtue" surrounds a magnet and extends in all directions around it. Other magnets and pieces of iron react to this orb of virtue and move or rotatein response. Magnets within the orb are attracted whereas those outside are unaffected. The source of the orb remained a mystery.

Source - University of Dallas, Department of Physics

Posted by Jay Roberts at 06:50 PM | Permalink

**Carl Friedrich Gauss **

Johann Carl Friedrich Gauss (April 30, 1777 - February 23, 1855) was a German mathematician, astronomer and physicist with a wide range of contributions; he is considered to be one of the leading mathematicians of all time.

Gauss was born in Brunswick (German Braunschweig), Duchy of Brunswick (now Germany) as only son of lower class uneducated parents. He impressed his teachers early on; the famous story is that in elementary school, the teacher tried to occupy the ever-inquisitive Gauss by telling him to add up the (whole) numbers from 1 to 100. Shortly thereafter, to the astonishment of all, the young Gauss produced the correct answer, having realized that pairwise addition of terms from opposite ends of the list yielded identical intermediate sums (1 + 100 = 101; 2 + 99 = 101; 3 + 98 = 101; 4 + 97 = 101, etc.).

Gauss earned a scholarship, and in college, he independently rediscovered several important theorems; his breakthrough occurred in 1796 when he correctly characterized all the regular polygons that can be constructed by ruler and compass alone, thereby completing work started by classical Greek mathematicians. Gauss was so pleased by this result that he requested that a regular 17-gon be inscribed on his tombstone.

He was the first to prove the fundamental theorem of algebra; in fact, he produced four entirely different proofs for this theorem over his lifetime, clarifying the concept of complex number considerably along the way. He also made important contributions to number theory with his 1801 book Disquisitiones arithmeticae, which contained a clean presentation of modular arithmetic and the first proof of the law of quadratic reciprocity.

At the same time, Gauss discovered the immensely important method of least squares which is used in all sciences to this day to minimize the impact of measurement error. He employed the least squares approach (without having yet disclosed it) to correctly predict the position of the asteroid Ceres. The method was later published in 1809 in a major work about the motion of celestial bodies.

He had been supported by a stipend from the Duke of Brunswick, but he did not appreciate the insecurity of this arrangement and also did not believe that mathematics is important enough to deserve to be supported; he therefore aimed for a position in astronomy, and in 1807 he was appointed professor of astronomy and director of the astronomical observatory in Göttingen.

Gauss discovered the possibility of non-Euclidean geometries but never published it. His friend Farkas Wolfgang Bolyai had tried in vain for many years to prove the parallel postulate from Euclid's other axioms of geometry and failed. Bolyai's son, János Bolyai, rediscovered non-Euclidean geometry in the 1820s; his work was published in 1832. Later, Gauss tried to determine whether the physical world is in fact Euclidean by measuring out huge triangles.

In 1818, Gauss started a geodesic survey of the state of Hanover, work which later lead to the development of the normal distribution for describing measurement errors and an interest in differential geometry and his theorema egregrium establishing an important property of the notion of curvature.

In 1831, a fruitful collaboration with the physics professor Wilhelm Weber devoloped, leading to results about magnetism, the discovery of Kirchhoff's laws in electricity and the construction of a primitive telegraph.

Even though Gauss never worked as a professor of mathematics and disliked teaching, several of his students turned out to be influential mathematicians, among them Richard Dedekind and Bernhard Riemann.

Gauss was deeply religious and conservative. He supported monarchy and opposed Napoleon whom he saw as an outgrowth of revolution. Gauss' personal life was overshadowed by the early death of his beloved first wife, Johanna Osthoff, in 1809, soon followed by the death of one child, Louis. Gauss plunged into a depression from which he never fully recoverd. He married again, to Friederica Wilhelmine Waldeck (Minna), but the second marriage does not seem to have been very happy. When his second wife died in 1831 after long illness, one of his daughters, Therese, took over the household and cared for Gauss until the end of his life. His mother lived in his house from 1812 until her death in 1839. He rarely if ever collaborated with other mathematicians and was considered aloof and austere by many.

Gauss had six children, three by each wife. With Johnanna (1780-1809), his children were Joseph (1806-1873), Wilhelmina (1808-1846) and Louis (1809-1810). Of all of Gauss' children, Wilhelmina was said to have come closest to his talent, but regrettably, she died young. With Minna Waldeck, he had three children: Eugene (1811-1896), Wilhelm (1813-1879) and Therese (1816-1864). Eugene emigrated to the United States about 1832 after a falling out with his father, eventually settling in St. Charles, Missouri, where he became a well respected member of the community. Wilhelm came to settle in Missouri somewhat later, starting as a farmer and later becoming wealthy in the shoe business in St. Louis. Therese kept house for Gauss until his death, after which she married.

He died in Göttingen, Hanover (now Germany).

Posted by Jay Roberts at 06:48 PM | Permalink

# Michael Faraday

**Michael Faraday** was born on September 22, 1791, near Elephant & Castle, London. At fourteen he apprenticed as a book-binder and during his seven year apprenticeship developed an interest in science.

After he sent Humphry Davy a sample of notes that he had made, Davy employed Faraday as his assistant. In a class-ridden society, he was not considered to be a gentleman, and it is said that Davy's wife refused to treat him as an equal and would not associate with him socially. His greatest work was with electricity. In 1821, soon after the Danish chemist, Ørsted, discovered the phenomenon of electromagnetism, Faraday built two devices to produce what he called electromagnetic rotation: that is a continuous circular motion from the circular magnetic force around a wire. Ten years later, in 1831, he began his great series of experiments in which he discovered electromagnetic induction. These experiments form the basis of modern electromagnetic technology.

In work on static electricity, Faraday demonstrated that the charge only resided on the exterior of a charged conductor, and exterior charge had no influence on anything enclosed within a conductor; this shielding effect is used in what is now known as a Faraday Cage.

He gave a successful series of lectures on the chemistry and physics of flames at the Royal Institution, entitled `*The Natural History of a candle*'; this was the origin of the Christmas lectures for young people that are still given there every year.

The unit of capacitance, the farad is named after him; his picture has been printed on British £20 banknotes.

He died at his house at Hampton Court on August 25, 1867.

Posted by Jay Roberts at 06:47 PM | Permalink

**Andre Marie Ampere **

André-Marie Ampère (1775 - 1836), French physicist, was born at Polemieux, near Lyons, on the 22nd of January 1775. He is generally credited as one of the main discoverers of electromagnetism. The ampere unit of measurement of electric current is named after him.

He took a passionate delight in the pursuit of knowledge from his very infancy, and is reported to have worked out long arithmetical sums by means of pebbles and biscuit crumbs before he knew the figures. His father began to teach him Latin, but ceased on discovering the boy's greater inclination and aptitude for mathematical studies. The young Ampère, however, soon resumed his Latin lessons, to enable him to master the works of Euler and Bernoulli. In later life he was accustomed to say that he knew as much about mathematics when he was eighteen as ever he knew; but his reading embraced nearly the whole round of knowledge--history, travels, poetry, philosophy and the natural sciences.

When Lyons was taken by the army of the Convention in 1793, the father of Ampère, who, holding the office of juge de paix had stood out resolutely against the previous revolutionary excesses, was at once thrown into prison and soon after perished on the scaffold. This event produced a profound impression on Andre-Marie's susceptible mind, and for more than a year he remained sunk in apathy. Then his interest was aroused by some letters on botany which fell into his hands, and from botany he turned to the study of the classic poets, and to the writing of verses himself.

In 1796 he met Julie Carron, and an attachment sprang up between them, the progress of which he naively recorded in a journal (Amorum). In 1799 they were married. From about 1796 Ampère gave private lessons at Lyons in mathematics, chemistry and languages; and in 1801 he removed to Bourg, as professor of physics and chemistry, leaving his ailing wife and infant son (Jean Jacques Ampere) at Lyons. She died in 1804, and he never recovered from the blow. In the same year he was appointed professor of mathematics at the lycée of Lyons.

His small treatise ''Considerations sur la theorie mathématique du jeu,'' which demonstrated that the chances of play are decidedly against the habitual gambler, published in 1802, brought him under the notice of J.-B.-J. Delambre, whose recommendation obtained for him the Lyons appointment, and afterwards (1804) a subordinate position in the polytechnic school at Paris, where he was elected professor of mathematics in 1809. Here he continued to prosecute his scientific researches and his multifarious studies with unabated diligence. He was admitted a member of the Institute in 1814.

It is on the service that he rendered to science in establishing the relations between electricity and magnetism, and in developing the science of electromagnetism, or, as be called it, electrodynamics, that Ampère's fame mainly rests. On the 11th of September 1820 he heard of H. C. Ørsted's discovery that a magnetic needle is acted on by a voltaic current. On the 18th of the same month he presented a paper to the Academy, containing a far more complete exposition of that and kindred phenomena.

The whole field thus opened up he explored with characteristic industry and care, and developed a mathematical theory which not only explained the electromagnetic phenomena already observed but also predicted many new ones.

His original memoirs on this subject may be found in the ''Ann. Chim. Phys.'' between 1820 and 1828. Late in life he prepared a remarkable Essai sur la philosophie des sciènces. In addition, he wrote a number of scientific memoirs and papers, including two on the integration of partial differential equations (Jour. École Polytechn. x., xi.).

He died at Marseilles on the 10th of June 1836 and is buried in the Cimetière de Montmartre, Paris. The great amiability and childlike simplicity of Ampère's character are well brought out in his Journal et correspondance (Paris, 1872). 45 years later, mathematicians recognized him.

Posted by Jay Roberts at 06:46 PM | Permalink

### History of Magnetism and Electricity

**600 BC - Lodestone**

The magnetic properties of natural ferric ferrite (Fe_{3}O_{4}) stones (lodestones) were described by Greek philosophers.

**600 BC**** ****- Electric Charge**

Amber is a yellowish, translucent mineral. As early as 600 BC the Greek philosopher, Aristophanes was aware of its peculiar property: when rubbed with a piece of fur, amber develops the ability to attract small pieces of material such as feathers. For centuries this strange, inexplicable property was thought to be unique to amber. This strange effect remained a mystery for over 2000 years, until, around AD 1600, Dr William Gilbert investigated the reactions of amber and magnets and first recorded the word 'Electric' in a report on the theory of magnetism.

Later in, in 1895, H.A. Lorentz developed the Electron Theory. We now know that there are three ways to generate electricity: Static, Electrochemical and Electromagnetic Induction.

**1175 - First Reference to a Compass**

Alexander Neckem an English monk of St. Albans describes the workings of a compass.

**1269 - First Detailed Description of a Compass**

Petrus Peregrinus de Marincourt, a French Crusader, describes a floating compass and a compass with a pivot point.

**1600**** ****- Static Electricity (De Magnete)**

In the 16th century, William Gilbert(1544-1603), the Court Physician to Queen Elizabeth I, proved that many other substances are electric (from the Greek word for amber, elektron) and that they have two electrical effects. When rubbed with fur, amber acquires resinous electricity; glass, however, when rubbed with silk, acquires vitreous electricity. Electricity repels the same kind and attracts the opposite kind of electricity. Scientists thought that the friction actually created the electricity (their word for charge). They did not realize that an equal amount of opposite electricity remained on the fur or silk. Dr. William Gilbert, realized that a force was created, when a piece of amber (resin) was rubbed with wool and attracted light objects. In describing this property today, we say that the amber is "electrified" or possesses and "electric charge". These terms are derived from the Greek word "electron" meaning amber and from this, the term "electricity" was developed. It was not until the end of the 19th century that this "something" was found to consist of negative electricity, known today as electrons.

Gilbert also studied magnetism and in 1600 wrote "De magnete" which gave the first rational explanation to the mysterious ability of the compass needle to point north-south: *the Earth itself was magnetic*. "De Magnete" opened the era of modern physics and astronomy and started a century marked by the great achievements of Galileo, Kepler, Newton and others.

Gilbert recorded three ways to magnetize a steel needle: by touch with a loadstone; by cold drawing in a North-South direction; and by exposure for a long time to the Earth's magnetic field while in a North-South orientation.

**1660 - Static Electricity Generator**

Otto von Guericke invents a crude machine for producing static electricity.

**1729 - Conductors and Nonconductors**

Stephen Gray describes that power possessed by one electrified body could be passed to another by connecting them.

**1734 - Electrical Attraction and Repulsion**

Read full story
Posted by Jay Roberts at 05:51 PM | Permalink